Gasoline, used as an automotive fuel in many automotive vehicles, is a volatile liquid subject to potentially rapid evaporation, in response to diurnal variations in the ambient temperature. Thus, the fuel contained in automobile gas tanks presents a major source of potential evaporative emission of hydrocarbons into the atmosphere. Such emissions from vehicles are termed ‘evaporative emissions’. The engine produces such vapors even if it is turned off.
Industry's response to this potential problem has been the incorporation of evaporative emission control systems (EVAP) into automobiles, to prevent fuel vapor from being discharged into the atmosphere. EVAP systems include a canister (the carbon canister) containing adsorbent carbon) that traps fuel vapor. Periodically, a purge cycle feeds the captured vapor to the intake manifold for combustion, thus reducing evaporative emissions.
Hybrid electric vehicles, including plug-in hybrid electric vehicles (HEV's or PHEV's), pose a particular problem for effectively controlling evaporative emissions with this kind of system. Although hybrid vehicles have been proposed and introduced having a number of forms, these designs share the characteristic of providing a combustion engine as backup to an electric motor. Primary power is provided by the electric motor, and careful attention to charging cycles can result in an operating profile in which the engine is only run for short periods. Systems in which the engine is only operated once or twice every few weeks are not uncommon. Purging the carbon canister can only occur when the engine is running, of course, and if the canister is not purged, the carbon pellets can become saturated, after which hydrocarbons will escape to the atmosphere, causing pollution.
A recirculation tube is an integral part of an EVAP system, and it is coupled to the fuel filler neck and the canister. During refueling, the recirculation tube recirculates fuel vapors into the fuel tank, rather than to the canister, which permits the canister size to be minimized. For vehicles having a bottom feeding fuel tank, vapor communication to the fuel filler neck may become blocked by the fuel at high fuel levels, which could cause leaks in the fuel cap area to be left undetected. Therefore, if a blockage occurs in the recirculation tube, the EVAP leakage detections systems may false pass any leakage in the fuel cap area. Therefore, monitoring the reliable operation of recirculation tubes is imperative in EVAP systems.
Considering the problems mentioned above, and other shortcomings in the art, there exists a need for an efficient system and method for identifying presence of any blockage in the recirculation tube of an EVAP system within a vehicle.